The Islamic State is "much stronger and much more dangerous" than anyone in the West realizes, according to the first Western journalist to be allowed extensive access to the group's territories, reported The Independent.

Jürgen Todenhöfer, a 74-year-old German journalist, just returned from a 10-day trip to Mosul, Iraq, the largest city occupied by the Islamic State, and is now reporting his findings to the world.

"We will conquer Europe one day. It is not a question of if we will conquer Europe, just a matter of when that will happen. But it is certain...For us, there is no such thing as borders. There are only front lines," a German ISIS spokesman and fighter told Todenhöfer, The International Business Times reported.

The spokesman continued, saying ISIS plans to conduct the "largest religious cleansing campaign" in history.

When asked what the group will do to the 150 million Shia who refuse to convert, the spokesman told Todenhöfer, "150 million, 200 million or 500 million, it does not matter to us. We will kill them all."

"Our expansion will be rapid and perpetual," he continued. "The Europeans need to know that when we come, it will not be in a nice way. It will be with our weapons. Those who do not convert to Islam or pay the Islamic tax will be killed."

Todenhöfer said he encountered "an almost ecstatic enthusiasm I have never encountered in any other war zone."

At one point, the journalist breached the topic of beheadings and enslavement, asking, "Do you seriously think that beheadings and enslavement actually signal progress for humanity?"

"Slavery absolutely signals progress," the man said, reported CNN. "Only ignorant people believe that there is no slavery among the Christians and the Jews. Of course there are woman who are forced into prostitution under the worst circumstances."

"I would say that slavery is a great help to us and we will continue to have slavery and beheadings, it is part of our religion ... many slaves have converted to Islam and have then been freed."

The spokesman blamed the beheading of journalists and aid workers on policies of the U.S., reported CNN.